The cylinder is then stamped around the neck
area indicating the month and year it was tested
along with the test station number.

Aluminum cylinders manufactured from 6351
aluminum are required to have an ultrasonic or eddy
current neck test every two years to inspect for
neck cracks that may have developed over time relating
to that grade of aluminum. This is indicated with E
stamped as part of the test stamp. It is sometimes
called a "Visual Plus" test after the
instrument used to conduct the test.

What Actually Happens?

When your scuba cylinder undergoes a visual
instection and hydrostatic test the following
will happen.

It is picked up from the Dive Shop by a cylinder
test station. Most shops do not have their own test
unit due to the economics involved in setup, annual
license fees, running costs, staff training along
with annual inspections by Quality Assurance.

Details of the cylinder are entered on a test
certificate: i.e. the cylinder number, the standard
to which it was manufactured, working pressure,
test pressure and the owner's details.

Visual Inspection

An external inspection is carried out looking
for damage or alterations that may include gouges,
dents or corrosion. Special attention is paid to
repainted cylinders as they may have been heat
treated or had dents and gouges filled. To carry
out this inspection thoroughly the cylinder boot
and mesh are removed. Dents, gouges, corrosion or
heat treating can all effect the integrity of this
high pressure vessel and they can fail test as a
result.

The cylinder is then drained and the valve
removed,. If in the opinion of the operator the
valve requires to be serviced it will usually be
serviced at an additional cost. The neck thread
and internal space is checked for corrosion, wear,
pitting or rust.

Older aluminum cylinders often fail
in this area as the neck thread may have corroded
or worn beyond the allowed tolerance, this is an
automatic failure under the standard. Aluminum
cylinders can also be badly corroded internally
especially if salt water has entered the cylinder.

Steel cylinders as we all know can be subject to rust,
some brands more than others due to the amount of
carbon used in the steel when manufactured.

It needs to be pointed out that rust in steel
cylinders is usually a result of carelessness by
its user or your fill station. If your cylinder
has been filled with moist air from a station
that has not been maintaining its filters or
compressor adequately rust will occur, oil may
also be found if this is the case.

Cylinders found to be rusty or corroded
internally and are not beyond repair are brushed
using various forms of wire brush attached to a
long shaft driven by an electric drill. The residue
is cleaned out and rumbling chips inserted into
the cylinder, it is then placed on a rumbler that
rotates the cylinder at about 90 to 100 rpm for
up to eight hours depending on the severity of
the corrosion. The cylinder is then filled with
water and inverted to assist in removing the
chips. It is then cleaned, dried and internally
inspected.

This time consuming process removes remaining
corrosion and polishes the internal cylinder wall
and is an additional cost.

Hydrostatic Testing

If the cylinder passes all the previous
inspections it is ready to be hydrostatically
tested, when it is filled with water and connected
to the test panel. The cylinder is pressurised
to fill pressure twice to check accuracy of
the panel and remove air bubbles from the system.

The cylinder is then pressurised to its test
pressure and held there for one minute. The pressure
is slowly released and the expansion measured on
a manometer tube. The maximum allowed expansion is
the water capacity of the cylinder in kilograms
divided by five.

The cylinder is disconnected from the test panel
and inverted to drain after which it is dried using
warm air. After a final internal inspection to ensure
proper drying the neck "o"ring is replaced
and the valve installed.

The cylinder is then stamped, filled, leak tested
at the neck and the test certificate completed.

How Much?

The price for a standard hydro or cylinder test
varies from shop to shop and test station. It generally
ranges between $25 and $55. Considering the process
involved and the fact that the cylinder is returned
full the value is exceptional.

Charges for ultrasonic neck inspections, rumbling
and valve servicing can also vary.

Helpful Hints

Your valve may not be serviced unless you ask
for it unless it is damaged, in poor condition and
noticed by the station operator.

Put your cylinder in for test at the end of the
month due on your test stamp, to be tested and
stamped with the next months date.

If you have your own compressor don't neglect
to have your cylinders tested annually. I recently
had an old aluminum cylinder in for test that hadn't been
tested for a number of years from a diver with his own
compressor. The size of the neck crack in that cylinder
scared the living daylights out of him and me both.

Scuba Doctor Service and Repairs is a specialised cylinder testing
and scuba gear service laboratory located at
3/106 Melbourne Road, Rye VIC 3941,
in the Rye Industrial Estate on the Mornington Peninsula. They are
open weekends and public holidays for divers convenience.
More about: Cylinder
Testing

Prices, specifications, and images are subject to change without notice.
We are not responsible for typographical or illustrative errors.
Some of our web prices are cheaper than in-store.
So please mention to our staff that you've seen them online.